We’re just done here. We’ve upgraded about every server from Windows Server 2008 R2 to Windows Server 2012 R2 and here are some of my experiences…
Upgrading vs. migrating
We chose to migrate most of the servers (i.e. setup a new server next to the old one and transfer the software) because this simply gave us the added advantage that we could use Generation 2 VMs vs Generation 1. Servers on generation 2 start a lot faster (really a LOT faster!) than their generation 1 counterparts but the running performance is about the same.
The system we did eventually upgrade was the Root CA (which is a server in a disconnected network) and the VM hosts. The upgrade process was simple, as long as you have SP1 installed in 2008 R2. (A system without this service pack simply cannot be upgraded without applying the service pack first.)
Installation times were relatively short and setting up features did not take much effort.
A note about Certificate Authorities
Certificate authorities cannot be migrated from one machine to another if they are also a domain controller. Even though there is a lengthy paper on this, migrating a CA is basically not a simple task. We eventually choose to remove the old one and setup a new one. Besides this, we did not ran into any issues.
The last things still on the list
We still need to do the database server, this one will be done in a couple of months from now. We’re also planning on removing a firewall (TMG is sadly a dead product now) and replacing this with some unix tech, I’ll write an article about this when I’ve got the time.